In the following documents some of the above problems are addressed, but no satisfactory solutions are presented.
U.S. Pat. No. 5,487,012 discloses a method for computer controlled production of an adaptive earpiece comprising at least one part, which is individually matched to the contours of an auditory canal. The method comprise the steps of tracing of the contours of the auditory canal to obtain contour data, digitization of the contour data and storage of the digitized values, converting the digitized values into a multi-dimensional computer model of the external contours of the adaptive earpiece and producing the earpiece on the basis of the computer model. The patent mentions that the tracing of the internal contours of the ear canal may be performed using ultra sound. The document further discloses a method for tracking the ear canal based on the use of an ear impression, but such a method would not resolve the problems relating to the usual way of producing shells as described above.
U.S. Pat. No. 5,056,204. In this document a method for producing a hearing aid, which is worn in the ear is described. The method comprise the steps of initially taking measurements of the inner space of the ear up to the eardrum for use in producing an individual shape of the body member corresponding with the measurements of the inner space of the ear. It is mentioned that the measurement is done by means of a laser. How this actually takes place is not disclosed.
PCT application WO 00/34739 discloses a method for manufacture of a hearing aid shell comprising a motor actuated ultrasonic probe used to acquire the shape data of the ear canal, an image processing computer, which also incorporates the driving electronics for the probe, with an edge detection algorithm used to filter the data. Thereby a digital image file of the three-dimensional topography of the ear canal is obtained. The ultrasonic probe is combined with a fiber optic probe used to monitor the position of the probe within the canal. The fiber optic probe comprises an inner coherent bundle of fibres and an objective lens that relay the image of the canal to a C.C.D. camera and an outer incoherent bundle of fibres that surround the coherent bundle and permits the illumination of the canal by an external light source that is optically coupled to the other end of the incoherent bundle. The position of the probe is determined solely by monitoring the displacement of the probe in one linear direction. Only the possibility of monitoring the motor, which is a step-motor is mentioned for this purpose. The probe is mounted on a stiff rod, and is not capable of following the possible bends of the ear canal. This limits the use of the probe, as many hearing-impaired people especially older people have ear canals with sharp bends.
Various methods and apparatuses for determining the internal properties of internal surfaces have been suggested, however none of these are useful when it comes to mapping the internal surface of a canal of the human body, in order to generate a digital model of the interior wall of the canal.
U.S. Pat. No. 5,004,339 discloses an apparatus for determining a characteristic of the inside surface of a bore comprising:    a guided wave fiber optic element capable of insertion into a bore;    a laser light source for directing light onto the proximal end of said fiber optic element;    means for directing light emanating from the distal end of said fiber optic element onto the inside surface of said bore and for directing light reflected from the inside surface of said bore onto the distal end of said fiber optic element; and    photo detector means capable of generating an output signal dependent upon light incident thereon;    means for directing light emanating from the proximal end of said fiber optic element onto said photo detector means whereby the output signal of said photo detector provides an indication of a characteristic of an inside surface of a bore. The patent further concerns a method for determining a characteristic of the inside surface of a bore using the above apparatus. The method may be employed on a body passage. Obtaining dimensional information concerning a cylindrical surface is mentioned, but not described in detail. Visualization of the bore wall of a sample is described. The sampled and held output of array video data is fed to the y and z axis of a storage video display with the x axis comprised by a pickoff of the movement along the bore length. No system for generating precise information concerning the position and orientation of the distal end of the fiber optic element is mentioned. The means for directing light from the distal end of the optic element onto the inside surface of the bore may be a mirror surface or a lens such as a wide-angle lens. The mirror surface can be designed to focus light on a point of the bore wall surface which is axially forward of the forward most portion of the mirror. This may be used to examine the bottommost portion of a blind bore. The patent does not mention the combined use of a mirror surface and a lens. Also the use of a semi-transparent mirror intended to direct part of the light to the circomferential surface and another part of the light to the surface which is axially forward of the mirror is not mentioned.
U.S. Pat. No. 5,469,245 relates to a method and an apparatus for measuring a three-dimensional position of a surface of a lengthwise object such as a pipe having a uniform cross section from a corresponding two-dimensional observed image of the object surface to measure, for example, the size of a defect in the surface. The patent does not mention systems to determine the exact location and orientation of a probe, which is inserted into the pipe.
U.S. Pat. No. 5,895,927 relates to a method and apparatus for profiling and dimensionalizing an interior cross-sectional portion of a tubular structure. The probe utilizes a disc of unfocused light to illuminate a cross-section of the interior surface and images the illuminated cross-section from the interior surface to a photo detector array, where the image can be evaluated. The photo detector array provides a continuous video signal, which can be fed to a video monitor and to a frame grabber. The resulting array of numbers can be processed by a computer program to find those pixels, which represent the illuminated cross-section, and through this, dimensional (diameter) data may be obtained. The patent does not mention systems for determining the position and orientation of the probe, in order to gain information relating to the length of the tubular structure or relating to possible bends in the tubular structure.
U.S. Pat. No. 6,073,043. This document describes a method and apparatus for determining the position and orientation of a remote object relative to a reference coordinate frame. The method and apparatus includes a plurality of field-generating elements for generating electromagnetic fields and a drive for applying signals to the generating elements. The signals generate a plurality of electromagnetic fields that are distinguishable from one another. The apparatus comprises a remote sensor having one or more field-sensing elements for sensing the fields generated and a processor for processing the outputs of the sensing element(s) into remote object position and orientation relative to the generating element reference coordinate frame. The position and orientation solution is based on the exact formulation of the magnetic field coupling. The system can be used for locating the end of a catheter or endoscope, digitizing objects for computer databases, virtual reality and motion tracking.